1. Field of the Invention
The field of the invention relates to systems for optical identification and verification of personal identity. More particularly, this invention relates to the optical scanning of fingerprints (dactyloscopical systems) for personal identification as required in such areas as computer technology, criminology, medicine, banking, finance, security, admittance-control systems and firearm safety locks.
2. Description of the Related Art
There are several prior art optical security systems which store, process and identify fingerprint patterns by electronic devices. Optical dactyloscopical systems can be divided into two groups according to their functional capabilities: (1) systems that read fingerprint images from intermediate data storage units, such as, for example, traditional dactyloscopical cards (fingerprint cards) and utilize various types of tables to classify the fingerprints (see MORPHO Systems leaflet of 1992); and (2) systems obtaining dactyloscopical information directly from the finger, i.e. the so-called xe2x80x9clive scanners.xe2x80x9d
These two groups differ greatly from each other. First, the surface texture of data storage units, which can be dactyloscopical cards or dermal ridge patterns of a fingertip, may differ. The area of application constitutes the second major difference between the two groups.
Systems of the first group are used mainly by police and criminologists for the purposes of personal identification of criminals. Dactyloscopical cards are used along with the tracks collected at a crime site. However, these systems are not suitable for immediate identity verification. Regular scanners such as designed by Morpho Systems, are currently used to read such dactocards and tracks (see MORPHO Systems leaflet of 1992). However, these types of systems cannot process information available from dermal ridge patterns of a live fingertip.
Moreover, the use of fingerprint cards causes a considerable loss of information because registration and processing of each and every small detail of dermal relief is limited.
Systems of the second group, which process optical dactyloscopical information obtained from a xe2x80x9clivexe2x80x9d finger, may be subdivided into the following categories:
Category 1xe2x80x94Systems operating in reflected light; and
Category 2xe2x80x94Systems operating in penetrating light.
This subdivision is based on the functional principles of the system at the initial stage of transformation of the dactyloscopical image. For example, over the last ten years, systems such as one designed by Digital Biometrics utilizes miniature cameras and charge transfer devices (CCDs) to detect the reflected part of light from a finger surface.
These reflection-type operating systems take advantage of the effects associated with the complete inner reflection of the light, i.e., light that is reflected just from those places of the prism surface at which the dermal ridges of a finger directly contact the prism surface.
The dactyloscopical camera uses a series of lenses to fix the reflected image of the dermal pattern. Such reflection systems have many advantages over systems utilizing dactocards. Reflection systems allow for quick scanning and processing of information, and a user""s fingers are not soiled from ink or ultraviolet-type stamping. However, these reflection systems also have some disadvantages due to their mode of operation. Some of these disadvantages are discussed below.
One disadvantage is that when a scanned finger is dry, the picture quality is reduced. This reduced quality results in a low probability of identification. The reason that a dry finger creates a problem is that when it touches the contact surface, the contact area is very small, making it impossible to produce a high-quality image. It has been proven that inaccuracy of at least one micron leads to a complete loss of dactyloscopical information. Such reflection systems attempt to compensate for this disadvantage by coating the contact surface with special contact substances, as disclosed in European Patent Application No. 304092, published Feb. 22, 1989. Another problem is that the low mechanical resistance of contact surface coatings causes the coating to come off after contact with several fingers.
Another disadvantage of using a series of lenses is that it principally leads to a significant drop in quality because of optical distortions and aberrations introduced by the lenses. Moreover, for each additional element introduced into the process of data transfer, additional errors are introduced. The use of a series of lenses enlarges the size of the device and decreases the mechanical stability and reliability. There have been attempts to seal hermetically the gaps between the lenses and the contact surface, especially to prevent loose particles from entering the gaps.
The above-mentioned disadvantages prevent widespread use of such reflection systems, allowing only for their occasional use in instances when neither the high security of automatic identification, nor the small dimensions of the device are prohibitive.
Russian Patent No. 2031625, published Mar. 27, 1995 discloses a light penetrating system and user identity verification method. In this system, a user""s finger must be placed on a fiber optical surface of camera, and then, penetrating directed at the finger. The output signal of the camera is computer processed, and thus the fingerprint is verified. When a finger comes into contact with an optical fiber, the dermal ridges fit closely with the fiber contact surface, and the light diaphaning the finger meets the contact surface and thus the photosensitive elements. The light lost and are much less at areas where the finger contact is direct, as opposed to areas where the relief structure does not allow direct contact.
The method disclosed in Russian Patent No. 2031625 generally is free from the types of disadvantages which are natural to light reflecting systems of image processing. The method disclosed by that Russian patent distinguishes over light reflecting systems by providing a better quality fingerprint image. The presentable gradations of dactyloscopical pictures depend only on the dynamic characteristics of the camera used. Additionally, the existence of gaps between the skin and a contact surface does not result in a complete loss of the information. Further, the size of this gap is proportional to the amount of penetrating light.
However, the light penetrating system also suffers from certain disadvantages. The present inventors have discovered that there are undesirable variations in the contrast of the dactyloscopical picture at the entry surface of the camera. These undesirable variations are caused by the user""s pulse, which provides variations in the bloodflow that affect the amount of light passing through the finger. Such instability of the image results in false pieces of information that decrease the quality of the image and increase the error rate.
Another disadvantage of the light penetrating system is the dependency of picture quality on the availability of outside natural light. Moreover, this prior art system does not distinguish between a live finger and a previously recorded fingerprint. Thus, the prior art light penetrating system is vulnerable to breach by a counterfeit image, making the system undesirable for use in code-locks and other security or access control systems.
Russian Patent No. 2031623 discloses a user identity verification system based on a camera with a fiber optical entry surface designed for finger contact. The finger placed on the entry area is diaphaned by a source of light or daylight, e.g. a liet bulb, which is installed opposite the contact surface. The camera is connected with a signal processing module.
Unlike the first type of light penetrating system, a device utilizing a fiber optical entry surface does not have any. lenses; therefore, it is free from all of the inaccuracies affecting identification introduced by aberrations of the optical lenses. Such devices are characterized by small dimensions, compactness, high reliability and an uncomplicated structure. As photosensitive units, they utilize charge transfer devices (e.g. CCD/chips) which are called Frame Transfer CCD (FTCCD). FT CCDs are configured separately. One-half of the FT CCD (the image section) is engaged in transformation of the light into an image by transforming light into charge quantity equivalents. The other half is used for storage and read out of the information (picture storage section). While the next image is being generated in the image creating section, the picture, storage section stores and reads out the previous image. Thus, in CCDs, the process of image creation and reading out takes place simultaneously.
The use of such CCDs guarantees high quality images. There are other types of two-section CCDs which are known to use different elements for creating the pictures and reading out the charge. One example employs elements scanning charge transfer image in lines (Interline Transfer CCD).
Devices using fiber optics for direct transmission of the image (without scale adaptation) are suitable for only rather small skin areas, and thus are insufficient for automatic identity verification. Tests have proved that for dactyloscopical identification, the fingerprint area has to be at least 16 mm in diagonal. Meanwhile, criminology standards in different countries usually require a diagonal of 24 mm for fingerprint analysis. However, the engineering of photosensitive units with a diagonal of 16-24 mm, in addition to using fiber optic entry and charge transfer devices for the complete image, encounters technically difficult problems at the present time.
There are fiber optical units with diameter adaptation, such as disclosed by Hamamatsu, which utilizes a fiber optical taper that allows for image enlargement. Such systems may be used as fiber optical lighting conductors in dactyloscopic devices. However, devices of this type cannot have a compact design. Moreover, the maximum resolution decreases to approximately five lines per millimeter, consequently raising the probability of fingerprint misidentification. Therefore, these devices are not suitable for practical use.
The above-described disadvantages of the prior art optical scanning identification devices and methods cause such devices and methods to be significantly limited in their potential use in automatic dactyloscopical identification processes due to a high probability of error, in a field where errors are critical. The disclosure of each of the above-cited references is incorporated by reference herein in its entirety.
An object of the present invention is to provide both a method and a device for a light penetrating system for user identification purposes which results in a reduction of the quality dependency of a fingerprint image from impairment by blood flow inside the finger and by outside natural light conditions. Improving the quality and informative value of the image causes a corresponding increase for more accurate identification. The probability of rate identification of errors is improved significantly.
The present inventors have discovered that diaphaning a finger with pulsating light leads to a considerable reduction of irregularity, instability and smearing or blurring of the output images and, consequently, of a video signal. This effect takes place due to the short pulses (approximately one ms). The negative effect of blood flow on the instability of the image of a finger becomes negligible. In addition, a reduction of the picture formation time period leads to a reduction of the negative influences of varying natural lighting conditions on the dactyloscopic picture of the dermal pattern as well. Thus, use of the pulsating light according to the present invention permits clean and sharply defined pictures, in contrast to the series of sometimes blurred pictures produced by the prior art system disclosed in Russian Patent No. 2031625. This improvement of the picture quality reduces the probability rate of identification errors.
In one embodiment of the present invention, a method for user identification by penetrating light comprises the steps of (a) placing a user""s finger on the fiber-optic entry surface of a video camera; (b) diaphaning the user""s finger with penetrating light; (c) generating a finger image signal by the video camera; and (d) processing an image signal transmitted from the video camera, where the finger is diaphaned by pulsating light as the video camera accumulates the image of a fingerprint in a picture formation mode.
Another embodiment of the present invention provides that before the placing of the user""s finger into the fiber optic input surface of the video camera, the user opens an access to the fiber optic surface and after identification, closes the access to the fiber optic input surface.
During the process of identification (i.e. when a user puts his finger on the entry surface of the camera), the finger is diaphaned by pulsating light, while the video camera is in the picture formation mode.
In another embodiment of the present invention, a video camera creates a sequence of pictures within a certain period of time. While processing these pictures, a signal-mean-value can be determined for each picture, or portions of the pictures may be selected. Thus, a time dependent sequence of signal-mean-values is determined and used as a criterion for user identification purposes.
In another embodiment of the present invention, an apparatus for user identification comprises a video camera with an optical input surface, the video camera including a photosensitive charge transfer device and a photosensitive device control module; a light source for outputting light for penetrating a section of the user""s finger; and a processing module that receives an output image from the video camera, where the light source is a pulsating light emitter which is synchronized with the photosensitive device control module for pulsating switching of the pulsating light emitter while the video camera is in an image accumulation mode and the photosensitive charge transfer device is one of a Full Frame CCD or a CMOS image sensor.
In another embodiment, the light penetrating identification device may comprise a photosensitive charge transfer device that is a CMOS image sensor with a full-frame electronic shutter as the photosensitive charge transfer device.
A Full Frame shutter permits switching to the CMOS image sensor in a flash and synchronizes with the pulse light source from the image accumulation mode into a storage and reading mode. This is necessary for receiving the fingerprint image during the pulse time without smearing or blurring.
In another embodiment, the light penetrating identification device may further comprise a controlling light driver connected between the photosensitive device control module and the pulsating light emitter. The light penetrating identification device may further comprise a cover as part of the light source, which covers the fiber optic input surface when the device is in a non-working mode, and uncovers the fiber optic input surface when the device is in a working mode. The light penetrating identification device may open the cover at an angle between 10 and 90 degrees from the fiber optic surface of the photosensitive device, when the device is in a working mode. In another embodiment the light source may comprise lighting elements placed along the finger of the user. The light source may comprise at least one pulsating light emitter, for example comprising light emitting diodes mounted, for example, onto the cover at a side that faces the photosensitive device.
The cover may be constructed for even reflection of light from the pulsating light emitter to the finger of a user. The light source may comprise at least one pulsating light emitter mounted onto the cover at a side which faces the photosensitive device, wherein the side of the cover is a mirror and the pulsating light emitter is located at a same plate with the photosensitive device.
In another embodiment, the light penetrating identification device may comprise a locking mechanism for securing and transforming the cover of the light source from a closed mode to an open mode. The cover may be made of a light non-transparent material and the design of the cover shields the fiber optic input surface of the camera from external lighting.
In another embodiment, the photosensitive unit is designed as a Full Frame CCD. The term Full Frame CCD means that the photosensitive unit does not have a special light-protected storage section. The picture-formation and the reading-out of the image are separate in time, not in space, as in Frame Transfer CCDs. Such devices are prevalent in the field of television engineering. In the Full Frame CCD, the procedures of picture formation and read out are just spatially separated, not temporally (in contrast to Frame Transfer CCDs).
The Full Frame CCD can be produced much cheaper and easier than the Frame Transfer CCD because it needs only half of the components (having the same dimensions of the photosensitive unit). Of course, the Full Frame CCD can not be exposed to permanent lighting through the object, because then the formation and read out of the pictures take place simultaneously, leading to an overlap of the pictures. The present invention solves this problem as follows. The devices are equipped additionally with a synchronized emitter to control the pulses of the lighting element. This emitter is installed between the lighting element and the control module of the photosensitive unit.
The processing of several consecutive pictures allows for an increase in the informative value of the dactyloscopical pictures, since further biometric data of the user is obtained (i.e., special features of pulse). This enhances the quality of the identity verification process. The use of a pulsating light emitter allows not only a far better quality of the dactyloscopical picture (as mentioned above), but also allows for the use of Full Frame CCDs as photosensitive units. Full Frame CCDs provide high quality pictures of larger areas. The enlargement of the area in focus along with the improved stability of the image leads to a further reduction of the error rate in the process of identification. The manufacture of Full Frame CCDs with a photosensitive area of 16-24 mm diagonal plus the fiber optical entry is an easy technical task, making the device relatively easy and cheap to produce. Further, Full Frame CCD devices distort less information, as compared to devices utilizing other methods of charge shifting.
As noted above, Full frame CCDs may not be used in devices working in permanent lighting, because the formation and read out of the pictures take place simultaneously leading to an overlap of the pictures. As a result, it is impossible to gain clear pictures. Thus, the present invention allows for high-quality pictures of fingerprints as an essential precondition of automatic identity verification, with a low error probability.
In another embodiment, the cover is a narrow bandpass optic filter which allows entry of light only from the light source. This filter can be situated in different places, for example, on a CCD or in a back side of a fiber optic plate. The filter function is analogical to the previous cover, because it protects from outside light and passes only light from the light source.